1. Field of the Invention
The present invention relates to an ejector mechanism for eccentric presses including a machine frame and a slide.
2. Brief Description of the Background of the Invention Including Prior Art
A preferred field of application of the present invention includes multi-stage presses for the production of preferably short metallic work pieces such as bolts, screws, shells, bushes and the like.
The invention is primarily concerned with a die side ejector pin, which has to eject a work piece during the return stroke of the slide. Rigorous requirements are applied to the ejection process. The ejected work piece has to be maintained in an unchanged position within the matrix, e.g., at a foremost position within the slide. The transporting device can grip the work piece only if the slide has been withdrawn. During the time period between the front slack point of the slide and the gripping of the raw pieces by the transport mechanism, the raw pieces have to be maintained in an unchanged position by an ejector on the piston side in order to ensure an error free positioning of the molded blank work pieces ahead of the next matrix.
A multi-stage press is known from British Patent GB-PS No. 1,079,300, which exhibits on the piston side an ejection mechanism with a pusher pin. The pusher pin is actuated by a lever, which is hinged at the slide. Upon a lift of the slide, the free end of the lever, which protrudes from the slide, glides over a curve on the machine frame. There are two regions of the curve that provide for a rest position of the pusher pin relative to the slide and also an intermediate region that effects the actual ejection.
By sliding the curve in the direction of the motion of the slide, not only is the stroke length of the pusher pin changed but also a phase shift of the pusher stroke lift is effected. The same holds for the backward final position, which changes with the adjustment of the stroke. In particular, this ejector mechanism is associated with the disadvantage that a resting of the work piece relative to the machine frame during the ejection process is not possible by sliding or shifting of the curve.
U.S. Pat. No. 3,364,721 to Criblez teaches an arrangement for controlling the movement of an auxiliary element on a crank operated device. The Criblez reference teaches the cooperation of levers and cams but does not refer to the ejection of work pieces.
British Pat. No. 2,141,958 to Stehr teaches an ejector device. The ejector device is operated according to the Figs. by a rotating cam device. However, the drawing does not show that a pusher pin is maintained with a spring and actuated by a lever, where the pusher pin retains a work piece in position.
U.S. Pat. No. 4,250,730 teaches a device for the ejection of a shaped work piece at the male die on a cross-feed press for non-cutting metal shaping. The reference teaches that the cam contour P of the cam disk has an arc K concentric to the rocker shaft and joined to straight section G and a runout section L. The reference teaches that a cam shaft is employed and that a cam is hingedly attached to the cam shaft for positioning a hinge that would push an ejector transfer rod 11. In view of the substantial geometric complexity of such an angled connection between a connecting rod and a cam, adjustment and precision of such device are limited.
British Pat. No. GB 2,023,473 A teaches an improved press. A carriage is mounted on a frame to be reciprocable relative to a die by a crankshaft such that a ram will work a work piece free. A bellcrank pivoted by a cam is employed to slide an ejector rod. The adjustment of a cam according to this reference is fairly complicated.
Swiss Pat. No. 472,962 teaches an ejector provision for mechanical presses with automatic ejection from the table and out of the press. The device as shown in the drawing includes several connecting rods and is rather involved for this kind of procedure. In particular, while a cam is employed in transferring the motion to a second pin, the control and adjustment of the motion according to this reference is fairly complicated, and also the precision is limited.
British Pat. No. 1,210,704 teaches mechanical power transmissions. The transmission of the reference includes a first crank mechanism having a first connecting rod for reciprocating a machine part and a second crank mechanism having a crank radius equal to the crank radius of the first crank mechanism and coupled to the first crank mechanism with its rotation axis arranged parallel with the axis of rotation of the first crank mechanism. The reference shows a fairly complex connection between an ejector mechanism and a cam operating lever.